Process of decolorizing sugar solutions with a porous quaternary ammonium anion exchanger



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United States Patent C PROCESS OF DECOLORIZING SUGAR SOLUTIONS WITH APOROUS QUATERNARY AMMONIUM ANION EXCHANGER Frederick H. Harding,Manhasset, and Frederick Bruder,

Ozone Park, N. Y., assignors to Rohm & Haas Company, Philadelphia, Pa.,a corporation of Delaware No Drawing. Application November 25, 1953,Serial No. 394,504

7 Claims. (Cl. 127-46) This invention relates to the manufacture ofrefined sugar solutions and refined sugar. It relates to the removal ofcolor-bodies from sugar solutionspreferably from hot sugar solutions-bymeans of strongly basic quaternary ammonium anion-exchange resins in thesalt form.

, It is conventional, in the manufacture of refined sugar solutions suchas syrups and of refined crystallized sugar, to treat sugar solutionsafter affination and clarification with a variety of sorbing materialssuch as bone-char or powdered carbon or other forms of carbon in aneffort to remove by absorption or adsorption the various extraneousmaterials which are present as impurities in the sucrose solutions. Thisis done because such impurities, including color-bodies, lower thequality of the syrups and reduce the quantity and/ or quality of thesugar which can be crystallized from the solutions.

It has also been shown, for example in U. S. Patents 2,551,519,2,578,937, 2,578,938 and 2,635,061, that vari ous combinations ofcation-exchange materials and quaternary ammonium anion-exchange resinsin the hydroxyl form can be used in the treatment of sugar solutions.

An object of this invention is to provide a methodof' purifying sugarsolutions which has commercial advantages over processes knownheretofore. An object is to provide a method which produces a betterquality 'of refined syrups and a greater yield of refined sugar andlower quantitiesof molasses. Still another object isto furnish a methodwhereby larger amounts of more con-- centrated sugar solutions can bedecolorized in a given evident are accomplished by the process of thisinvention which comprises treating-preferably at elevated temperatures-asolution of sucrose which contains colorbodies with a quaternaryammonium anion-exchange resin which is in the salt form.

In the preferred embodiment of this invention, a hot sucrose solution,which may or may not contain some invert sugar and which does containcolor-bodies, is passed through a bed or layer of particles of aquaternary ammonium anion-exchange resin in the chloride form.Colorbodies are adsorbed on the resin and anions in solution,particularly sulfate, phosphate and carbonate ions, are simultaneouslyexchanged for chloride ions on theresin. When the resin has adsorbed itsfull capacity as evidenced by the fact that the efiluent sugar. solutionis not sufiiciently lighter in color than the influent solution theresin is considered exhausted and requires regeneration. The sugarsolution remaining in the bed of resin is drained off and the layer ofresin is rinsed with water. The resin is then treated with aqueoussolutions of sodium chloride and sodium hypochlorite which remove thecolor-bodies, replace the adsorbed anions with chlon'deions, andrestoreice the resin to its original condition. Rinsing with wateror preferablywith a dilute solution of ammonium hydroxidecompletes the cycle.

While the description above is that of the preferred embodiment it isevident from the following discussion that variations in the process canbe made without depart: ing from the spirit of the invention.

The process of this invention can be applied to any sugar solutionhowever dark in color and it will efiect a real reduction in color. Itis more reasonable, however, to apply the process to sugar solutionswhich have been alfinated and also clarified with lime and phosphates.At least seventy percent of the color can be removed from such asolution by a single rapid treatment with the resin. Since otheradsorbents such as bone-char, activated'charcoal and powdered carbonalso remove substantial quantities of color-bodiesbut not all-and sincetheir use up to a point is economical it is also practical to use themfirst to remove the color bodies which are most readily adsorbed andthen to remove essentially all of the remaining color-bodies byadsorption on the quaternary ammonium ion-exchange resin. It appearsthat the ion-exchange resins have a specificity for the color-bodieswhich are least readily adsorbed by conventional adsorbents andtherefore they can be used most advantageously to remove the finaltraces of color from sugar solutions which have been partiallydecolorized.

The ion-exchange resins which are employed are those which containquaternary ammonium salt groupspreferably chloride groupsas their polargroups. They are cross-linked, and hence insoluble, resins in granularor preferably spheroidal form and they contain in their structurequaternary ammonium salt groups. The quaternary ammonium salt groups arethe functional groups on which adsorption of the anions take place andadsorption of the color-bodies is also believed to take place. Suchresins are well known and are available commercially. Suitable resinsare those which are made, for example, according to the processes of U.S. Patents 2,591,573 and 2,614,099 by first forming an insoluble,cross-linked copolymer of a monovinyl hydrocarbon and a copolymerizablecrosslinking agent such as divinylbenzene, then haloalkylating thecopolymer whereby alkylene halide groups become joined to the insolublecopolymer and finally aminating the haloalkylated resin with a tertiaryamine such as trimethylamine or dimethylamino ethanol. Other quaternaryammonium anion-exchange resins are made by the process of U. S. Patent2,540,985. While quaternary ammonium resins are ordinarily sold in thebasic or hydroxyl form they are readily converted to the salt form bytreatment with a solution of an inorganic salt or mineral acid.

What is required here is an insoluble quaternary ammonium anion-exchangeresin of the strongly basic type which is in the salt form. What is alsodesired is that the resin be as porous as possible. As is well known,the degree of porosity of such a resin is inversely proportional to theamount of cross-linking agent which is employed and accordingly it isrecommended that the quaternary ammonium anion-exchange resin be aslowly cross-linked as is consistent with other required properties suchas insolubility and degree of swellability. For example, in the case ofthe resins which are made by the processes of U. S. Patents 2,591,573and 2,614,099, it is most desirable that the amount of copolymerizedcross-linker be not over 4% and preferably from about 0.5% to about 2%on a molar basis. Here again, resins of this kind are availablecommercially as quaternary ammonium anion-exchange resins of the porousgrade. '7

When employed in this process of sugar refining the resin is in the saltform-preferably in the chloride form. It can also be used in the bromideform which is fully crystallized sugar than chlorides and also causeturbid-- ity in the syrups. The quaternary ammonium anionexchange resinin the chloride form not only adsorbs color-bodies but also. exchangesits chloride. ions for. sulfate ions. This is most advantageous becausesugars. of lower ashecontent are obtained, presumably because chlo-.ride salt re not occluded so tenaciously by sugar crystals asare fsu vate salts and can befar more. readilyremoved.

Itis much preferred thatthe sugar solutions which-are Pyliified by; this1 process be hot. .When the process-is operated at -elevatedtemperatures the volume of sucrose solution w 1c ,can betreated withagivenamount of resin; in any g ventime, is far greater than. when lowtemperatures are employed. Also of .real importance is the. fact thatrnpre concentrated solutionscan. be purified. Syrups at atemperaturewithinthe rangeof 130 to.2 l- B. have been treated anddecolorized very successfully,. but,it is. preferred thatthetemperatureof the solutionsbef rom lm" to 190-F. Undertheseconditio ns solutionshaving a concentration at leastas high as about. joffiBrix, have beenrapidly and efficiently puri-' color-bodiesand other anions andultimately becomese xhaju sted. At this point it is freed of thesugarsolution is usually rinsed, and is then regenerated. Two inds ofregenerants are required to restore thesresin to its original condition;namely a solution .of a waters olub le Salton-mineral acidv and .asolution of. a. mild oxidigin'g agent. While .these two kinds ofregenerants can be mixed in the same. solution. it is preferred thatthey be used-separately, Thefirst kind of.regenerantifhichs isordinarily sodium. chloride or sulfuric -acid s adsorbed; anions ,butfailsto remove all of the ed color-bodies from; the .resin. Thecolor-bodies are removed Afte eatment with the two .kinds of I regenerants the r in s in condition to. treat and purifymoresugar l ilQr...

Sodium; chloride solutions are much preferred as regenerants and thesecan be of any reasonable andlconve'nient concentration, .Inpractice itis preferred to. employ solutions containing about 1% ,to 15% salt.Solutions of Qth'er witter-soluble chlorides such as hydrochloric acid,potassium chloride, calcium chloride and magnesium chloridehave beenused but these have no'advantage over solutions of sodiumchloride. Whatis evident from this h o weven is that acheap sodium chloride brinewhich contains other water-solublechlorides as impurities can be usedifdesired. Hot solutions of sodium chloride at 130? toabout 2 00 F, areparticularly efficient.

iqcause .the watensoluble chloride regenerant alone doe not remove ,allof the color-bodiesand hence fails instselftorestorethe resin to itsfull capacity, it is nece ss ary .to employ in .adiiitiona solution of amild oxidib in g agent suchas a solution of a water-soluble hypo haliteparticularly a .hypochlorite-.or asolution of hydrogen peroxide.Solutions of sodium hypochlorite are QCOngmended .although otherhypohalites such as potassiumhypochlorite, potassiumhypobromite,sodium-hypo:

, however, by .the mild oxidizingagent.

bromite and calcium hypochlorite can likewise be used.

. Strong oxidizing agents. including potassiumepermangw nate, nitricacid and chromic acid have also been used; and while these are effectivein removing the color-bodies they are less satisfactory than thehypochlorites or hydrogen peroxide because they; tend, to degrade theresins. Solutions containing up to peroxideor sodium hypochlorite havebeen used but the particular concentration employed is a matter ofchoice. Usually. more dilute solutions are preferred.

Under those conditions: where the-quantities of -color-- bodies in thesugar solutions are high'andthe amounts which are adsorbed are also highin comparison with the amounts of other anions which. are-simultaneouslyadsorbed, it is suggested;thatregeneration with both salt and oxidizingagent be carried out each time the resin becomes exhausted. In suchcases it appears best to treat the exhausted resin first with a hotsolution containing about 1% to 1 0%. of the mineralacidor-salt thereof,then with a 0.25%. to 5%- solution ofah'ypochlorite or ofhydrogenperoxide at room-or ambient temperature and then again with ahot solution of the mineral acid or salt.

On the other hand, when the ratio of adsorbed colorbodies to otheradsorbed anions is low,- it may be-preferred, to regenerate the resin anumber of-times with only a mineral acid or salt of a mineral acid,allow the color-bodies to accumulate, and then only occasionally toregeneratewith the mild oxidizing agent.

In any case what is required is that theexhaustedresin be regeneratedwith an aqueous solution of a mineral acid; or a salt thereof.preferablywith a solution of sodium chloride-insofar as is possible and that-thecolor-bodies whichare adsorbed more tenaeiously and which are notremoved by the first regenerant be removed by means of a solution of amild oxidizing agent.

Thefollowing examples serve to further illustrate this invention. In theexamples the colors which are recorded are based on the AmericanMolasses Companys Color Standards which are described in AnalyticalChemistry, vol. 2.4, page 832 (May 1952).

Example 1 andiin ally: reacting the chloromethylated copolymer: withtrirnethylarnine. The column of resin beadswas 2.4- inches. ingdepth.The sugar solution-was flowed at a-rateof '62i5 gals. per square foot ofcolumn area per hour. A'total quantity of sugar solution equivalent to1500.pounds of solid sugar per-cubicyioot of resinwas passed through thecolumn. The efiiuent had aconcentration. of 58'.7 Brix, .a pH of 5.9, ;acolor-of 3. and contained 3.3. color units- Thus,. a;total of 88.5%ofthe colorhadbeenremoyedo The-ionexchange resin was regeneratedasfollows:v A 10% .aqueous solution of sodiurnrchloride, aha-tempera tureof,175 F., was slowly percolated throughtheibedrof resinover a-totalcontact time of 20 minutes. The bed of resinwas then washed thoroughly.with water.

The whole procedurewhich comprisesthe treatment of the sugar solution,the removal of the color therefrom. and 'the regeneration of the resinconstitutes onecycleof operation.

Example 2 Th ,B QQ'iSS. .of, .-Example ,1 was repeated fl mesin avenuesthe manner described, with essentially the same kind of washed raw sugarmelt. The 75th cycle was run as follows: A washed raw sugar melt havinga concentration of 60 Brix, a pH of 7.0, a color of 16, and containing31 color units was percolated through the same column of anion-exchangeresins. Here, as in the previous cycles, a total quantity of sugarsolution equivalent to 1500 pounds of solid sugar per cubic foot ofresin was passed through the column of resin at a rate of 62.5 gals/sq.ft./hour. The efliuent had a concentration of 59 Brix, a pH of 6.3, acolor of 6+, and contained 6.2 units of color.

It will be noted that about 80% of the color was removed. While thisrepresents a real and very worthwhile improvement in the quality of thesugar solutions it is not as great a removal as was obtained in earliercycles. The gradual loss of the capacity of the resin to removecolor-bodies is due to the fact that some of the colorbodies are notremoved from the resin by the step of regeneration, as explained above.

In this case, however, the same column of resin was used for 75 morecycles in the same manner described above. In the 150th cycle the sameequivalent amount of washed raw sugar melt was passed through the samecolumn of resin at the same rate and at the same temperature. Theinfluent had a concentration of 60 Brix, a pH of 7, a color of 16+, andcontained 32 color units. The effluent had a concentration of 59 Brix, apH of 6.2, a color of 10+, and contained 8.6 color units. In this cycleabout 73% of the color was removed.

After the sugar solution had drained from the column of resin and thelatter had been rinsed with hot water (sweetening off) the resin wasregenerated as follows: A 10% aqueous solution of sodium chloride, at atemperature of 175 F., was slowly percolated through the bed of resinover a total contact time of 20 minutes. The bed of resin was thoroughlyrinsed first with hot water and then with cold Water. Next the bed wastreated with a 2% aqueous solution of sodium hypochlorite at 80 F. for atotal contact time of 60 minutes. Finally the column of resin wasthoroughly rinsed with hot water.

In the 151st cycle, after the bed of resin had been regenerated withsodium chloride and with sodium hypoohlorite as above described, awashed raw sugar melt was decolorized. The influent had a temperature of180 F., a concentration of 60 Brix, a pH of 7.1, a color of andcontained 26 color units. The quantity of sugar solution and rate offlow were the same as described in Example 1. The efiiuent had aconcentration of 59 Brix, a pH of 6.2, a color of 5, and contained 5.2color units. In this cycle approximately 80% of the color was removed.This represents an improvement over the results of cycle No. 150 andshows the value and importance of using an oxidizing agent, at leastperiodically, in the regeneration of the ion-exchange resins.

Treatment of sugar solutions was continued in the manner described aboveusing the same column of resin, the same rate of fiow, the sameregenerating procedure with sodium chloride every cycle and alsoemploying the regenerating procedure with sodium chloride and sodiumhypochlorite every thirtieth cycle. In the 410th cycle over 74% of thecolor was removed.

Example 3 The purpose of this example is to compare the decolorizingability of a quaternary ammonium anion-exchange resin in the chlorideform with that of powdered activated carbon. The same washed raw sugarmelt was employed and initially it had a concentration of 60 Brix, a pHof 7.0, a color of 16 and contained 31 color units.

A portion of this solution was treated in the conventional manner withpowdered activated carbon in an amount equal to 1% of the weight ofsolid sugar in the solution. The resultant solution had a color of 9 andcontained 8 units of color indicating that 74% of the color had beenremoved by the carbon.

Another portion of the washed raw sugar melt was treated in exactly themanner described above in Example 1. The product had a color of 3+ andcontained 3.5 color units indicating that the resin had removed morethan 88% of the color.

Example 4 A partially decolorized and filtered whole raw sugar melthaving a concentration of 62 Brix, a pH of 5.5, a color of 22 andcontaining 123 color units was passed at a temperature of 170 F. througha column of anionexchange resin in the chloride form. The resin was thethe same quaternary ammonium chloride resin described and employed inExample 1 above and the rate of flow was 71.2 gals/sq. ft./hr. An amountequivalent to 320 pounds of solid sugar per cubic foot of resin was thustreated. The efiluent had a concentration of 60.0 Brix, a pH of 5.7, acolor of 13 and contained 14.0 color units. From this it is evident that88.7% of the color had been removed by the resin.

Example 5 In some cases, particularly where the quantities ofcolor-bodies to be removed by the resin are high and many of thecolor-bodies are adsorbed tenaciously and are not removed by salt oracid alone during regeneration, it is preferred to regenerate the resinevery cycle with a mild oxidizing agent, such as hydrogen peroxide orsodium hypochlorite. In such cases a very dilute so-. lution ofoxidizing agent can be used and/or the time of contact of the oxidizingagent with the resin can be decreased.

Accordingly, many portions of a washed raw sugar melt were passedthrough a column of the anion-exchange resin described in Example 1above. The solutions all had an average concentration of 60 Brix, a pHof about 7.0, a color of 16-17, and contained about 31-34 color units.They were passed through the column at the rate of 62.5 gals/sq.ft./hour until the equivalent of 1500 lbs. of solid sugar had passedthrough per cubic foot of resin. The resin was then regenerated by meansof a 2.5% aqueous solution of sodium chloride at 175 F. during a contacttime of 20 minutes and with .a 0.25% aqueous solution of sodiumhypochlorite at F. during a contact time of 20 minutes, followed in eachcase by thorough rinsing with water.

The efiluent from the 75th cycle had a color of 3+ and contained 3.5color units, indicating a removal of color. The effluent from the 150thcycle had a color of 3-4 and contained 3.7 color units, thus showingthat 88% of the initial color had been removed.

We claim:

1. The process of purifying a sucrose solution which contains dissolvedimpurities including color-bodies which comprises bringing saidsolution, at a temperature from F. to 210 E, into contact with a porousquaternary ammonium anion-exchange resin which is in the salt form.

2. The process of purifying a sucrose solution which contains dissolvedimpurities including color-bodies which comprises bringing saidsolution, at a temperature from 130 F. to 210 F., into contact with aporous quaternary ammonium anion-exchange resin which is in the chlorideform.

3. The process of purifying an afiinated and clarified sucrose solutionwhich contains dissolved impurities including color-bodies whichcomprises bringing said solution, at a temperature from 130 F. to 210F., into contact with a porous quaternary ammonium anion-exchange resinwhich is in the chloride form.

4. The process of purifying a sucrose solution which contains dissolvedimpurities including color-bodies which comprises passing said solutionat a temperature from 130 F. to 210 F. through a layer of particles of aporous quaternary ammonium anion-exchange resin which islinnthechloride.= form, thereby removing. said colorzbodies frornsaid-solutionand adsorbing themlon said" resin, separating-the. resultant solutionfrom said resirLandT finally: regenerating said resin and removingsaidadsorbed color-bodies from it by treating it With a solution of aWater-Soluble chloride and with a solution of a mild oxidizing agent.

5. The process of purifying a sucrose solution which contains? dissolvedimpurities including color-bodies which comprises passing said solutionatl a temperature from 140T'FJ. to 190 F. through awla yer of particlesof a porous quaternary ammonium anion-exchange resin which is.in-the'chloride form, thereby removing said color-bodies from said solutionand adsorbing them on said .resin,. separating the resultant solutionfrom said resin and finally regenerating said resin and removingsaidia'dsorbed color-bodiesirom it by treating it with a solution of aWater-soluble chloride and with a solution offa mild oxidizingaagent.

61The process of purifying an aflinated and clarified sucrose solutionwhich is at a concentration of 40 to about 70 Brix and Which containsdissolved impurities including color-bodies which comprises passing saidsolution at'a'temperature'from 140 F. to 190 F. through a layer: ofparticles of a porous quaternary ammonium anion-exchange resin inthechloride form, thereby removingsaid color-bodies from said'solution andadsorbingfthem'on said-resin, separating the resultant'solutionfrom'saidresin and finally regenerating said resin and saidiadsorbedcolor-bodies from it by treating it with a: solution of sodiumchlorideand with an solution of sodium hypochlorite 7; The process of -purifyingan afiinatedand clarified said adsorbed color-bodies from it by treatingit with a solution of sodium-chloride and with a solution-of 2 hydrogenperoiide.

' ReferencesCited'in the file of this patent UNITED STATES PATENTS2,578,938 Kunin Dec. 18, 1951 2,650,177 Menard-"mm Aug. 25, 1953 FOREIGNPATENTS 489,173 Great Britain Jan; 20, 1937 OTHER REFERENCES Serial N6.359,575, Sinit (AP. 0. published May 11,1943.

1. THE PROCESS OF PURIFIYING A SUCROSE SOLUTION WHICH CONTAINS DISSOLVEDIMPURITIES INCLUDING COLOR-BODIES WHICH COMPRISES BRINGING SAIDSOLUTION, AT A TEMPERATURE FROM 130* F. TO 210* F., INTO CONTACT WITH APROOUS QUATERNARY AMMONIUM ANION-EXCHANGE RESIN WHICH IS IN THE SALTFORM.